Chalcogen-mediated band tuning, optoelectronic and transport properties of LaCuXO (X = Se, Te) Oxychalcogenides: First-principles study

Abstract

Density functional theory (DFT) analyzes the electronic, optical, and thermoelectric properties of LaCuSeO and LaCuTeO oxychalcogenides, illustrating their multifunctional semiconductor potential. Structural optimizations confirm their tetragonal P4/nmm symmetry, with stable bonding properties impacted by the heavier, more polarizable Te atoms, which improve lattice cohesion and thermodynamic stability specifically in LaCuTeO. Direct energy band gaps at the Γ point were noticed, with better predictions via the TB-mBJ potential providing values of 1.88 eV and 1.44 eV for LaCuSeO and LaCuTeO, respectively. The valence bands are largely occupied by Cu-3d and chalcogen-p orbitals, whereas the conduction bands mostly comprise La-d states. Optical investigation reveals substantial visible-range absorption, static dielectric constants of 7.0–8.0, and refractive indices of 2.7–2.8, suggesting good transparency and light-harvesting properties. Distinct peaks in the dielectric functions and absorption spectra correspond to interband transitions, with LaCuTeO having stronger optical transitions resulting from its smaller band gap and greater polarizability. Thermoelectric study using Boltzmann transport theory shows that Seebeck coefficients rise with temperature, peaking up to 4.2 μV/K at 650 K. Electrical conductivity and electronic thermal conductivity also show temperature-dependent trends, indicating inherent semiconductor properties. At 650 K, the computed dimensionless figure of merit (ZT) of LaCuSeO and LaCuTeO peaks at 0.85 and 0.83, respectively, because of their excellent ZT and low thermal conductivity. These results highlight LaCuSeO and LaCuTeO as interesting choices for thermoelectric energy conversion, transparent electronics, and optoelectronic applications, while they have nominal band gaps, good carrier transport, and multifunctional capability in a single-phase material system.